Multiple CSI reports for multi-user superposition transmission

ABSTRACT

According to an aspect, a radio access network node supports the transmission of multi-user superposition transmissions, where multi-user superposition transmission comprises transmitting, in each of a plurality of time-frequency resource elements, a modulation symbol intended for a first UE and a modulation symbol intended for a second UE, using the same antennas and the same antenna precoding. The radio access network node receives multiple CSI reports from the first UE for a first reporting instance. One or more of the received multiple CSI reports correspond to one or more respective multi-user superposition transmission states. The radio access network node also determines whether to use multi-user superposition transmission or an orthogonal multiple access transmission for scheduling the first UE in a first scheduling interval, based on the received multiple CSI reports.

TECHNICAL FIELD

The present disclosure generally relates to communication networks, andmore particularly relates to channel state information, CSI, reports formulti-user superposition transmission, or MUST.

BACKGROUND

Multi-user superposition transmission, or MUST, schemes with differentflavors are being studied in the context of Long Term Evolution, LTE,Release 13. In general, MUST can be realized by superposing the dataintended for different UEs at different transmit power levels in thesame time-frequency resources, such as Orthogonal Frequency DivisionMultiplexing, OFDM, resource elements. The total power is split amongthe UEs served in the same time-frequency resources, where the transmitpower level allocated to a given UE (or ‘power share values’) isgenerally determined by the channel condition (i.e., path loss)experienced by the UEs. For instance, UEs having higher path loss (i.e.,cell edge UEs) can be allocated higher transmit power levels while UEshaving lower path loss (i.e., cell center UEs) can be allocated lowertransmit power share values.

FIG. 1 shows a simplified block diagram of a MUST transmitter configuredto superpose transmitted symbols for two UEs. As shown in the figure,the information bits corresponding to the near UE (i.e., the cell-centerUE) and those corresponding to the far UE (i.e., the cell-edge UE) arefirst separately channel encoded. The two sets of channel encoded bitsare then jointly modulated and precoded with the appropriate transmitpower level settings to produce the MUST signal. Generally, a highertransmit power level is allocated to the far UE and a lower transmitpower level is allocated to the near UE. The total transmit power iskept unchanged compared to the case where all the transmit poweravailable within a data transmission resource in a single subframe isallocated to a single UE.

FIG. 2 shows a simplified block diagram of MUST receiver processing fora case with two superposed UEs. Since the two UEs are allocateddifferent power levels, the near UE can attempt to cancel theinterference emanating from the data transmission intended to the farUE.

Typically, the far UE uses a normal receiver and need not even be awarethat there is a superposed transmission to a near UE. The interferencecancellation for the near UE can be done in two ways. A first option isthat the codeword corresponding to the far UE is decoded at the near UEand then reconstructed and cancelled or removed from the receivedsignal. This type of cancellation is referred to as codeword levelinterference cancellation, CWIC, in FIG. 2. A second option is that thenear UE makes a symbol-wise hard demodulation decision of the symbolscorresponding to the far UE and then cancels the interference. In FIG.2, this type of interference cancellation is referred to as symbol levelinterference cancellation, SLIC.

Following the steps of interference cancellation, the near UE thendecodes its own codeword(s). For certain flavors of MUST schemes, athird option is also possible where the near UE collects its own codedbits (i.e., discards the far UE coded bits) and then proceeds towardsdecoding its own codeword(s).

Given that the far UE is allocated a higher transmit power level thanthe near UE, the far UE demodulates and decodes its own codeword withoutcancelling the interference emanating from the data transmissionintended to the near UE.

Three variants of MUST schemes are being considered in the Release 13study item on MUST. Brief descriptions of these schemes are given below.

Non-Orthogonal Multiple Access (NOMA)

In the NOMA scheme, the information bits corresponding to the far UE andthe near UE are independently encoded and modulated. Let x_(N) and x_(F)denote the coded modulation symbols of near UE and far UE, respectively.The symbol x_(N) is drawn from a near UE constellation

_(N), and the symbol x_(F) is drawn from a far UE constellation

_(F). Then the superposed symbol x_(S) in the NOMA scheme is given byx _(S) =√{square root over (α)}x _(N)+√{square root over (1−α)}x _(F)  Equation 1

where 0<α<1 represents the fraction of power allocated to the near UE.The superposed constellation

_(S) is labeled ass=n+f|

N|   Equation 2

where |

_(N)| is the number of bits/symbol in the near UE constellation, n and frespectively represent the labels of the near and far constellations. Anexample of the superposed NOMA constellation for the case where both thenear UE and far UE employ QPSK constellation is shown in FIG. 3. Sincetwo QPSK constellations are used, the superposed constellation issimilar to 16 QAM (depending on the value of a).

Semi-Orthogonal Multiple Access (SOMA) SOMA differs from the NOMA schemein that SOMA uses Gray mapped superposed constellation. The codedmodulation symbols of near UE and far UE are Gray mapped and then addedtogether as in Equation 1. An example of the superposed SOMAconstellation for the case where both the near UE and far UE employ QPSKconstellation is shown in FIG. 4.Rate-Adaptive Constellation Expansion Multiple Access (REMA)

REMA is similar to SOMA with one restriction that the resultingsuperposed constellation

_(S) should be a regular QAM constellation having equal horizontal andvertical spacing between constellation points (as is used in e.g. LTE).In REMA, the bits with the higher bit-level capacities are allocated forthe far UE and the bits with the lower bit-level capacities areallocated for the near UE. In addition, the power sharing parameter αshould also be set appropriately so that the resulting superposedconstellation is a regular QAM constellation. There are six differentways (shown in Table 1) of realizing REMA that has LTE standardconstellations as superposed constellations.

TABLE 1 REMA Superposed Constellations Superposed Near UE Near UE PowerConstellation Far UE Constellation Constellation Share α in dB  16-QAMQPSK QPSK  −6.9867 dB  64-QAM QPSK 16-QAM  −6.2342 dB  64-QAM 16-QAMQPSK −13.1876 dB 256-QAM QPSK 64-QAM  −6.0730 dB 256-QAM 16-QAM 16-QAM−12.2915 dB 256-QAM 64-QAM QPSK −19.2082 dBSystem Model

When multiple antennas are used on the transmitter side, a transmitprecoder, v, must be used, that defines how a symbol is transmitted fromeach of the multiple transmit antennas. A precoder thus contains theamplitude scaling and phase adjustment of the symbol at each of thetransmit antennas. Precoding implies that beamforming gain can beachieved.

Generally, it is possible to apply different precoders to the near andfar UEs in the NOMA scheme. However, in the receiver processing of thenear UE in FIG. 2, the application of different precoders implies thatthe near UE has to acquire knowledge of the precoder applied to the farUE either via blind detection or explicit signalling. To simplify thenear UE receiver processing, it is desirable to apply the same precoderto both the near and far UE.

Now assuming the application of the same precoder to both the near andfar UEs, the generalized received signal model is derived for MUSTschemes. It is assumed the radio access network node or eNodeB isequipped with N_(Tx) transmit antennas and each UE has N_(Rx) receiveantennas. Assuming P to be the total transmit power per sub-carrier, letαP and (1−α)P respectively denote the transmit powers allocated to thenear UE and the far UE.

For simplicity of presentation, it is assumed that each UE receives arank-1 transmission stream. Then, the transmitted signal correspondingto the k^(th) resource element, RE, can be written asx _(S)(k)=√{square root over (αP)}v(k)x _(N)(k)+√{square root over((1−α)P)}v(k)x _(F)(k)   Equation 3

where x_(N)(k) and x_(F)(k) denote the coded modulation symbols of nearand far UEs at the k^(th) RE, respectively. Furthermore, v(k) representsthe N_(Tx)-element rank-1 precoder corresponding to the transmittedstream (note that the same precoder is applied to both UEs).

If the N_(Rx)×N_(Tx) physical channel of the near UE is represented asH_(N)(k), then the combined channel perceived by the near UE can bewritten asg _(N)(k)=H _(N)(k)v(k).   Equation 4

The N_(Rx)-dimensional received signal vector corresponding to the nearUE is given byy _(N)(k)=H _(N)(k)x _(S)(k)+w _(N)(k),   Equation 5

where w_(N)(k) includes the noise plus inter-cell interferenceexperienced by the near UE at the k^(th) RE. Using Equation 3-Equation 4in Equation 5, the received signal vector of the near UE can be given asy _(N)(k)=√{square root over (αP)}g _(N)(k)x _(N)(k)+√{square root over((1−α)P)}g _(N)(k)x _(F)(k)+w _(N)(k).   Equation 6

In MUST schemes, the near UE can try to cancel the interferencecomponent √{square root over ((1−α)P)}g_(N)(k)x_(F)(k), since α<0.5. Inthe NOMA and SOMA schemes, the near UE can use either the CWIC or theSLIC receiver for this interference cancellation as shown in FIG. 2. Dueto the regular QAM structure of REMA's superposed constellation, thenear UE in the REMA case can simply use its own coded bits to decode itsown codeword (see FIG. 2).

Similarly, if the N_(Rx)×N_(Tx) physical channel of the far UE isrepresented as H_(F)(k), then the combined channel perceived by the farUE can be written asg _(F)(k)=H _(F)(k)v(k).   Equation 7

The N_(Rx)-dimensional received signal vector corresponding to the farUE is given byy _(F)(k)=H _(F)(k)x _(S)(k)+w _(F)(k),   Equation 8

where w_(F)(k) includes the noise plus inter-cell interferenceexperienced by the far UE at the k^(th) RE. Using Equation 3 andEquation 7 in Equation 8, the received signal vector of the far UE canbe given asy _(F)(k)=/√{square root over ((1−α)P)}g _(F)(k)x _(F)(k)+√{square rootover (αP)}g _(F)(k)x _(N)(k)+w _(F)(k).   Equation 9

In MUST schemes, the far UE does not cancel the interference component√{square root over (αP)}g_(F)(k)x_(N)(k) owing to the fact that α<0.5.Hence, the far UE's total interference and noise term is given by√{square root over (αP)}g_(F)(k)x_(N)(k)+w_(F)(k). The far UE receiverprocessing is depicted in FIG. 2.

Channel State Information Feedback and Scheduling

In one scheme, the existing implicit channel state information, CSI,with a single CQI report per UE is used in MUST scheduling. Theterminology orthogonal multiple access, OMA, is used in this scheme torefer to Orthogonal Frequency-Division Multiple Access. OFDMA, which isused in current LTE (i.e., OMA refers to both Single-User-Multiple InputMultiple Output, SU-MIMO, and Multi-User-Multiple Input Multiple Output,MU-MIMO, as currently defined in LTE). In this scheme, each UE within acell reports a single channel quality information, CQI, assuming fulltransmission power is allocated to that UE during data transmission. Inother words, the single CQI report from each UE assumes OMA operation.The scheduling methodology of this scheme for each scheduling band(either wideband or subband) can be summarized as follows:

-   -   Step 1: The scheduler first selects two UEs (UE₁ and UE₂)        belonging to the serving cell with corresponding single CQI        reports CQI_(UE1) and CQI_(UE2). If CQI_(UE1) is sufficiently        higher than CQI_(UE2), then UE₁ is designated as the near UE and        UE₂ is designated as the far UE. In this step, it may also be        important to check the combination of precoders among these UEs        when deciding that UE₁ and UE₂ can be valid MUST pairs (i.e., if        UE₁ and UE₂ have reported the same precoder). This is done by        comparing the two PMIs corresponding to CQI_(UE1) and CQI_(UE2)        reported by the two UEs.    -   Step 2: If UE₁ and UE₂ are deemed a valid MUST pair, select a        near UE power share parameter α from a set A of predetermined        power share parameter values (i.e., α∈A).    -   Step 3: For the selected a value, calculate the scheduling        Signal to Interference-plus-Noise Ratios, SINRs, for MUST,        SINR_(UE1) and SINR_(UE2), using CQI reports CQI_(UE1) and        CQI_(UE2) with the following approximations.        -   UE₁'s scheduling SINR for MUST is calculated as            SINR′_(UE) ₁ =α×SINR_(UE1)   Equation 10        -   UE₂'s scheduling SINR for MUST is calculated as

$\begin{matrix}{{SINR}_{{UE}_{2}}^{i} = \frac{\left( {1 - \alpha} \right)}{\alpha + \frac{1}{{SINR}_{{UE}\; 2}}}} & {{Equation}\mspace{14mu} 11\mspace{14mu} 1}\end{matrix}$

-   -   Step 4: The scheduler then calculates the MUST proportional fair        (PF) metric corresponding to the MUST UE pair under        consideration as

$\begin{matrix}{\sum\limits_{{UE}_{i} \in U}\left( \frac{R\left( {\left. i \middle| U \right.,\alpha} \right)}{L(i)} \right)} & {{Equation}\mspace{14mu} 12}\end{matrix}$

-   -   where R(i|U, α) and L(i) respectively denote the instantaneous        throughput and the average throughput of UE_(i). In Equation 12,        R(i|U, α) is a function of MUST scheduling SINRs computed in        Equation 10-Equation 11, and hence R(i|U, α) also depends on the        power share parameter α. The candidate user set U contains the        MUST UE pair under consideration.    -   Step 5: The steps 1-4 are repeated for all valid MUST UE pairs        with all power share parameter α values in the set A.        Additionally, the OMA PF metrics corresponding to each UE        belonging to the serving cell are also calculated as currently        done in LTE.    -   Step 6: From Step 5, the scheduler decides whether OMA or MUST        should be employed in the current scheduling band depending on        which scheme provides the highest PF rate. The UE(s)        corresponding to the highest PF metric are scheduled. In case        the MUST scheme is scheduled in the scheduling band, the power        share parameter value that yields the highest PF rate is chosen.

SUMMARY

One of the problems with the existing approach of relying on a singleOMA CQI report per UE for MUST is the rank mismatch that could arise dueto the difference in the power allocated to the UE in MUST mode whencompared to the OMA mode. This problem is particularly prominent in nearUEs since the near UE power share α is typically chosen to be lower than0.5.

Consider an example near UE with good channel conditions that isallocated a power share of α=0.1 for MUST. Due to the good channelconditions, the near UE will most likely recommend a rank-2 transmission(i.e., two spatial layers) with the corresponding CQI and PrecodingMatrix Indicator, PMI, in its OMA CQI report. However, in MUST mode,where the near UE is only allocated 10% of the power it gets in the OMAmode, the near UE may not be able to successfully receive a rank-2transmission. In this case, it would have been better to schedule thisnear UE in MUST mode with a rank-1 transmission. The existing approachdescribed above does not address this issue of rank mismatch.

Another related problem with the existing approach is the issue of CQImismatch whenever there is rank mismatch between the OMA mode and theMUST mode. In the existing approach, the MUST scheduling SINRs for thenear UE is derived via the simple scaling operation of Equation 10 usingthe reported OMA CQI. Assuming ideal interference cancellation at thenear UE, such scaling is accurate only if there is no rank mismatchbetween the OMA mode and the MUST mode. However, if there is a rankmismatch between the OMA and MUST mode, using the approach in Equation10 will result in a CQI mismatch. For instance, revisiting the abovementioned rank mismatch example, the OMA mode has a rank of two and theMUST mode has a rank of one. In this case, the existing approach willresult in a CQI mismatch because the rank-2 CQI report (obtained fromthe single OMA CQI) takes into account inter-layer interference and thisis not compensated for in the simple scaling operation of Equation 10.

A third problem with the existing scheme is that whenever there is rankmismatch between the OMA mode and the MUST mode, there will also likelybe PMI mismatch. This could result in missed MUST pairing opportunitiesfor MUST schemes that apply the same precoder to both the near and farUEs.

Hence, in accordance with the principles of the present invention,various embodiments are provided for allowing multiple CSI reports to besent by the UE for the purpose of MUST. The multiple CSI reports maycorrespond to different data transmission power levels, different rankrestrictions, or different precoders with the best and the second bestmeasured quality CQI values. In addition, the embodiments describedifferent ways of using the multiple CQI reports to identify valid MUSTUE pairs.

According to some embodiments, a method, in a radio access network nodeconfigured to support the transmission of multi-user superpositiontransmissions, where multi-user superposition transmission comprisestransmitting, in each of a plurality of time-frequency resourceelements, a modulation symbol intended for a first user equipment, UE,and a modulation symbol intended for a second UE, using the sameantennas and the same antenna precoding, includes receiving multiplechannel-state information, CSI, reports from the first UE for a firstreporting instance. One or more of the received multiple CSI reportscorrespond to one or more respective multi-user superpositiontransmission states. The method also includes determining whether to usemulti-user superposition transmission or an orthogonal multiple accesstransmission for scheduling the first UE in a first scheduling interval,based on the received multiple CSI reports.

According to some embodiments, a method, in a first UE configured tosupport the transmission of multi-user superposition transmissions,where multi-user superposition transmission comprises transmitting, ineach of a plurality of time-frequency resource elements, a modulationsymbol intended for the first UE and a modulation symbol intended for asecond UE, using the same antennas and the same antenna precoding,includes sending multiple CSI reports for a first reporting instance.One or more of the received multiple CSI reports correspond to one ormore respective multi-user superposition transmission states.

According to other embodiments, a method is performed by a radio accessnetwork node configured to support the transmission of multi-usersuperposition transmissions, where multi-user superposition transmissioncomprises transmitting, in each of a plurality of time-frequencyresource elements, a modulation symbol intended for a first UE and amodulation symbol intended for a second UE, using the same antennas andthe same antenna precoding. This method comprises receiving a CSI reportfrom the first UE, the received CSI report being based on an assumptionthat a transmission power for a physical channel is lower than a minimumtransmission power that is assumed when multi-user superpositiontransmission is not used. The method further comprises transmitting amulti-user superposition transmission to the UE, where said transmittingis based on the received CSI report.

Correspondingly, according to other embodiments, a method is performedin a UE configured to support the transmission of multi-usersuperposition transmissions, again where multi-user superpositiontransmission comprises transmitting, in each of a plurality oftime-frequency resource elements, a modulation symbol intended for thefirst UE and a modulation symbol intended for a second UE, using thesame antennas and the same antenna precoding. This method comprisesreceiving one or more configuration messages from a radio access networknode, the one or more configuration messages directing the UE totransmit a CSI report, the one or more configuration messages comprisingat least one of (a) a selected parameter indicating a ratio of aPhysical Downlink Shared Channel (PDSCH) energy per resource element toa CSI reference symbol (CSI-RS) energy per resource element, wherein theselected parameter is selected from a range having a minimum valuecorresponding to a ratio below −8 dB, or (b) a selected parameterindicating a ratio of a PDSCH energy per resource element to acell-specific reference symbol (CRS) energy per resource element,wherein the selected parameter is selected from an extended range havinga minimum value corresponding to a ratio below −6 dB. The method furtherincludes transmitting a CSI report, in accordance with the one or moreconfiguration messages, and receiving a multi-user superpositiontransmission from the radio access network node.

Still other embodiments include a radio access network node configuredto support the transmission of multi-user superposition transmissions,where the radio access network node comprises a transceiver circuitconfigured to send and receive transmissions; a receiving module forreceiving a CSI report from the first UE, the received CSI report beingbased on an assumption that a transmission power for a physical channelis lower than a minimum transmission power that is assumed whenmulti-user superposition transmission is not used, where the transceivercircuit is configured to transmit a multi-user superpositiontransmission to the UE, based on the received CSI report. Likewise,other embodiments include a UE configured to support the transmission ofmulti-user superposition transmissions, the UE comprising a transceivercircuit configured to send and receive transmissions, including aconfigured to receive a multi-user superposition transmission from aradio access network node, and a receiving module for receiving one ormore configuration messages from the radio access network node, the oneor more configuration messages directing the UE to transmit a CSIreport, the one or more configuration messages comprising at least oneof (a) a selected parameter indicating a ratio of a PDSCH energy perresource element to a CSI-RS energy per resource element, wherein theselected parameter is selected from a range having a minimum valuecorresponding to a ratio below −8 dB, or (b) a selected parameterindicating a ratio of a PDSCH energy per resource element to a CRSenergy per resource element, where the selected parameter is selectedfrom an extended range having a minimum value corresponding to a ratiobelow −6 dB. The UE further comprises a sending module for sending,using the transceiver circuit, a CSI report, in accordance with the oneor more configuration messages.

According to some embodiments, a radio access network node is configuredto support the transmission of multi-user superposition transmissions,where multi-user superposition transmission comprises transmitting, ineach of a plurality of time-frequency resource elements, a modulationsymbol intended for a first UE and a modulation symbol intended for asecond UE, using the same antennas and the same antenna precoding. Theradio access network node includes a transceiver circuit configured tosend and receive transmissions, and a processing circuit. The processingcircuit is configured to receive, via the transceiver circuit, multipleCSI reports from the first UE for a first reporting instance. One ormore of the received multiple CSI reports correspond to one or morerespective multi-user superposition transmission states. The processingcircuit is configured to determine whether to use multi-usersuperposition transmission or an orthogonal multiple access transmissionfor scheduling the first UE in a first scheduling interval, based on thereceived multiple CSI reports.

According to some embodiments, a first UE is configured to support thetransmission of multi-user superposition transmissions, where multi-usersuperposition transmission comprises transmitting, in each of aplurality of time-frequency resource elements, a modulation symbolintended for the first UE and a modulation symbol intended for a secondUE, using the same antennas and the same antenna precoding. The UEincludes a transceiver circuit configured to send and receivetransmissions, and a processing circuit. The processing circuit isconfigured to send, via the transceiver circuit, multiple CSI reportsfor a first reporting instance. One or more of the received multiple CSIreports correspond to one or more respective multi-user superpositiontransmission states.

According to some embodiments, computer readable storage medium andcomputer programs may be executed on processing circuitry to perform oneor more of the above methods.

Of course, the present invention is not limited to the above featuresand advantages. Indeed, those skilled in the art will recognizeadditional features and advantages upon reading the following detaileddescription, and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a generalized illustration of a MUST transmitter with twosuperposed UEs.

FIG. 2 is a generalized illustration of MUST receiver processing withtwo superposed information streams intended for two UEs respectively.

FIG. 3 illustrates an example of superposed NOMA constellation.

FIG. 4 illustrates another example of superposed SOMA constellation.

FIG. 5 illustrates an example of 16-QAM superposed REMA constellation.

FIG. 6 illustrates a request-based CQI reporting by a UE with multipleRI/PMT/CQI configurations for MUST transmission, according to someembodiments.

FIG. 7 illustrates a block diagram of a radio access network node,according to some embodiments.

FIG. 8 illustrates a method of receiving multiple CSI reports fordetermining whether to use multi-user superposition transmission or anorthogonal multiple access transmission, according to some embodiments.

FIG. 9 illustrates a block diagram of a UE, according to someembodiments.

FIG. 10 illustrates a method of sending multiple CSI reports, accordingto some embodiments.

FIG. 11 illustrates an example functional implementation of a radioaccess network node, according to some embodiments.

FIG. 12 illustrates an example functional implementation of a UE,according to some embodiments.

FIG. 13 is a process flow diagram illustrating an example methodaccording to some embodiments.

FIG. 14 is a process flow diagram illustrating another example methodaccording to some embodiments.

DETAILED DESCRIPTION

Reference may be made below to specific elements, numbered in accordancewith the attached figures. The discussion below should be taken to beexemplary in nature, and not as limiting of the scope of the presentinvention. The scope of the present invention is defined in the claims,and should not be considered as limited by the implementation detailsdescribed below, which as one skilled in the art will appreciate, can bemodified by replacing elements with equivalent functional elements.

Embodiments of the present invention provide for allowing multiple CSIreports to be sent by the UE for the purpose of MUST. The multiple CSIreports may correspond to different data transmission power levels,different rank restrictions, or different precoders with the best andthe second best measured quality CQI values.

For example, a radio access network node, such as an LTE eNodeB, or eNB,is configured to support the transmission of multi-user superpositiontransmissions, where multi-user superposition transmission comprisestransmitting, in each of a plurality of time-frequency resourceelements, a modulation symbol intended for a first UE and a modulationsymbol intended for a second UE, using the same antennas and the sameantenna precoding. The radio access network node receives multiple CSIreports from the first UE for a first reporting instance. One or more ofthe received multiple CSI reports correspond to different possiblemulti-user superposition transmission states, where a multi-usersuperposition transmission state is a particular combination ofallocated transmission power and transmit antenna precoding. Thedifferent possible multi-user superposition transmission states may foeexample be one or more respective multi-user superposition transmissionstates corresponding to the one or more of the received multiple CSIreports. The radio access network node is also configured to determinewhether to use multi-user superposition transmission or orthogonalmultiple access transmission for scheduling the first UE in a firstscheduling interval, based on the received multiple CSI reports.

Multiple CSI reports of a reporting instance can be considered to beassociated with one another, in that they generally correspond to thesame interval of time and/or the same radio channel measurements.Reporting instances may be periodic, according to configurationinstructions provided to the UE, but in some embodiments may also orinstead be aperiodic, in response to a request from the radio accessnetwork node or another node.

Example methods of receiving multiple CSI reports include where theprecoding matrix indicators, PMIs, of the multiple CSI reports from oneUE that correspond to different data transmission power levels,different rank restrictions, or different qualities are compared to aPMI of another CSI report from another UE for the purpose of identifyingvalid MUST UE pairs.

In some cases, the first UE can be configured to send CSIs when the UEis configured to receive multi-user superposition transmissions. Thiscan include, for example, providing a power ratio value selected from afirst set of power ratio values, where the first set of power ratiovalues contains smaller power ratios than a second set of power ratiovalues, and where the second set of power ratio values may be used forUEs that are not configured to receive multi-user superpositiontransmissions, and where the power ratios are ratios of PDSCH energy toreference signal energy. In this case, Physical Downlink Shared Channel,PDSCH, can be extended to a reference signal energy per resourceelement, RS EPRE, ratio range in CSI reports.

In another example, the first UE can be configured to report multipleCSIs when the UE is configured to receive multi-user superpositiontransmissions, where multi-user superposition transmission comprisestransmitting a modulation symbol intended for a second UE using the sameprecoding and on the same antennas as a modulation symbol intended forthe UE. A plurality of parameters corresponding to different potentialmulti-user superposition transmission states can be provided, theplurality of parameters comprising a set of transmission powers, a setof transmission rank restrictions, and/or a set of precoderrestrictions.

It is noted that for some cases one of the CSI reports is not specificto MUST, perhaps to support dynamic switching between MUST and non-MUSTtransmissions. In other cases, the UE may not receive an explicitconfiguration message specific to MUST. In such cases, the existingsignaling, not specific to MUST, can be used to realize rank restrictedmultiple CSI reports.

Continuing with the example of configuring the UE, in some cases,superposition hypotheses may only include serving PDSCH parameters,where superposition is defined as using the same precoding. All of theparameters may indicate one or more potential states of a transmissionintended for the UE. In other examples, the UE is configured to send themultiple CSI reports aperiodically when requested by the eNodeB. EachCSI report may correspond to different data transmission power levels.

Additional examples include methods where one of the CSI reportscorresponds to full data transmission power level (this corresponds toOMA CQI, which is important for dynamic switching between OMA and MUST).The UE may assume ideal interference cancellation for the CSI reportscorresponding to non-full data transmission power levels. Each CSIreport may correspond to different rank restrictions or CSI measurementsof different quality.

Methods may include indicating a configuration of multiple CSI reportsto a UE for the purposes of MUST where each configuration indication maycontain one or more of a power ratio parameter with extended range tosupport MUST (radio resource control, RRC, signaling), a list of powerratio parameters with extended range to support MUST (RRC signaling),and/or a bit string indicating the restricted set of precoders to beconsidered during CSI measurements and feedback.

In some embodiments, a signal corresponding to the interference from afirst UE to a second UE is transmitted on the interference measurementresource of the second UE where the first UE is configured to receivemulti-user superposition transmissions. The interference component istransmitted using the same precoding and on the same antennas as themodulation symbols intended for the first and second UEs.

Three embodiments will be described in more detail below, but ingeneral, it should be understood that multi-user superposition isdistinct from multi-user multiple-input and multiple-output, MIMO, asused in LTE in that for multi-user superposition transmissions, the sameantenna patterns and precoding (or “same effective antenna”) are usedfor the transmissions intended for the different UEs. Multi-user MIMO,on the other hand, relies on spatial multiplexing between the users,which is achieved by using different antennas and/or antenna precoding.To facilitate multi-user superposition transmissions, the CSI feedbackshould accurately predict the needed transmission parameters to obtaingood downlink throughput given this same effective antenna behavior

CSI feedback comprises at least channel quality information, CQI,indicating a modulation and coding rate that could be used for a PDSCHtransmitted to the UE providing the feedback at a predetermined blockerror rate. A CSI report may also comprise additional feedback such asprecoding matrix indications, rank indications, etc. Therefore, in somecases, a UE is configured to send multiple CSI reports for the purposeof multi-user superposition transmission. The CSI reports may compriseat least a channel quality indication.

In some instances, a plurality of parameters corresponding to differentpotential multi-user superposition transmission states are hypothesizedin CSI feedback. In general, the amount of feedback overhead and UEcomputational complexity grows in proportion to the number of parametersand multi-user transmission states for which the UE provides CSIfeedback. Therefore, it is generally desirable to provide a small numberof parameters that provides as much performance gain as possible.

If N parameter settings are jointly and independently hypothesized for Musers in a multi-user transmission, the number of parameter settings ison the order of N^(M). One approach to avoiding this exponential growthof the number of parameter hypotheses is to provide parameterscorresponding only to hypotheses of the PDSCH intended for the UE,rather than those for both the intended and interfering PDSCHs, and tohave the UE assume that single user transmission is used. In this case,it is still possible to have accurate CSI feedback when an interferingPDSCH is transmitted, so long as it is transmitted in the same way(i.e., using the precoding, etc.) as the desired PDSCH. This allowsdynamic switching between multi-user superposition and single-usertransmission.

Because parameters or the presence of the interfering far UEtransmission are not part of the hypotheses, the UE should calculate theCSI assuming that a superposed far UE PDSCH does not interfere with thereceived near UE PDSCH. Therefore, in some embodiments, when calculatingthe MUST specific CQIs, a UE that employs interference cancellation(i.e., a ‘near’ UE, UE₁) may assume that the interference component inEquation 6 can be completely cancelled.

Example Embodiment 1

A first embodiment will now be described in more detail. In thisembodiment, an eNodeB generally configures the UE(s) to send multipleCSI reports where one of the CSI reports corresponds to the OMA mode andone or more other CSI reports correspond to the MUST mode. Having oneCSI report for OMA and one or more CSI report(s) for MUST ensures thatthe proposed solution supports dynamic switching between OMA and MUSTmodes. That is, the scheduler in the proposed scheme can more accuratelydecide whether OMA or MUST should be employed in a given scheduling banddepending on which scheme provides the highest PF rate. To reduce uplinkfeedback overhead, the eNodeB may configure only the near UE(s) to sendmultiple CSI reports for the purposes of MUST; the far UE(s) may beconfigured to send only a single OMA CSI report. The eNodeB may useReference Signal Received Power, RSRP, reports and/or uplink pathlossmeasurements to distinguish between the near and far UEs.

The eNodeB configures the OMA CSI report such that full transmissionpower allocation is assumed when the UE measures CQI. In the CSIreport(s) configured specifically for MUST, the eNodeB configures theUE(s) such that each of the MUST specific CQIs corresponds to adifferent power share value. The steps involved in this embodiment aresummarized below. Although these steps are described using one near UEand one far UE, the solution proposed in this embodiment is applicableto a plurality of near and far UEs.

Step 1:

The eNodeB configures a near UE UE₁ to send Q>1 CSI reports. One of thereports contains a CQI denoted by CQI_(UE1) ⁰ that corresponds to theOMA CQI (i.e., assumes full transmission power). The remaining Q−1 CSIreports contain CQIs denoted by CQI_(UE1) ¹, CQI_(UE2) ², . . . ,CQI_(UE1) ^(Q−1) that respectively correspond to Q−1 different MUSTpower share values α₁, α₂, . . . , α_(Q−1) (note that α₁, α₂, . . . ,α_(Q−1) are assumed to be in non-decreasing order here). Additionally,the eNodeB configures a far UE UE₂ to send a single OMA CSI reportcontaining a CQI that is denoted by CQI_(UE2) ⁰.

Step 2:

UE₁ calculates the CSI reports (including the CQIs) according to thepower share hypotheses, and then sends the Q CSI reports to the eNodeB.Similarly, UE₂ sends the OMA CSI report to the eNodeB. When calculatingthe MUST specific CSIs, UE₁ may assume that the interference componentin Equation 6 can be completely cancelled.

Step 3:

For each scheduling band, the eNodeB scheduler first checks if CQI_(UE1)⁰ is sufficiently higher than CQI_(UE2) ⁰. Additionally, the schedulerchecks the combination of precoders among these UEs when decidingwhether UE₁ and UE₂ can be valid MUST pairs. This is done by comparingthe PMI corresponding to CQI_(UE2) ⁰ with the PMIs corresponding toCQI_(UE1) ¹, CQI_(UE1) ², . . . , CQI_(UE1) ^(Q−1). If the PMI ofCQI_(UE2) ⁰ matches or is sufficiently close to the PMI of CQI_(UE1)^(q) where 1≤q≤(Q−1), then UE₁ and UE₂ can be valid MUST pairs with nearUE power share parameter close to α_(q).

Step 4:

If UE₁ and UE₂ are deemed a valid MUST pair, then the eNodeB schedulercan select a near UE power share parameter {tilde over (α)} close toα_(q). The parameter {tilde over (α)} is selected from a set A ofpredetermined power share parameter values (i.e., {tilde over (α)}∈A).

Step 5:

For the selected C value, calculate the scheduling SINRs for MUST usingSINR_(UE) ₁ and SINR_(UE) ₂ , corresponding to CQI reports CQI_(UE1)^(q) and CQI_(UE2) ⁰ with the following approximations:

-   -   UE₁'s scheduling SINR for MUST is calculated as

$\begin{matrix}{\frac{\overset{\sim}{\alpha}}{\alpha_{q}} \times {SINR}_{{UE}\; 1}^{q}} & {{Equation}\mspace{14mu} 13}\end{matrix}$

-   -   UE₂'s scheduling SINR for MUST is calculated as

$\begin{matrix}\frac{1 - \overset{\sim}{\alpha}}{\overset{\sim}{\alpha} + \frac{1}{{SINR}_{{UE}\; 2}^{0}}} & {{Equation}\mspace{14mu} 14}\end{matrix}$

Step 6:

The scheduler then calculates the MUST PF metric corresponding to theMUST UE pair under consideration as

$\begin{matrix}{\sum\limits_{{UE}_{i} \in U}\left( \frac{R\left( {\left. i \middle| U \right.,\overset{\sim}{\alpha},\alpha_{q}} \right)}{L(i)} \right)} & {{Equation}\mspace{14mu} 15}\end{matrix}$

where R(i|U, {acute over (α)}, α_(q)) and L(i) respectively denote theinstantaneous throughput and the average throughput of UE_(i). InEquation 15, R(i|U, {tilde over (α)}, α_(q)) is a function of MUSTscheduling SINRs computed in Equation 13-Equation 14, and hence R(i|U,{tilde over (α)}, α_(q)) also depends on the power share parameters{tilde over (α)} and α_(q). The candidate user set U contains the MUSTUE pair under consideration.

Step 7:

The steps 3-6 are repeated for all valid MUST UE pairs with all α_(q)that yield matching PMIs and all {tilde over (α)} values in the set A.Additionally, the OMA PF metrics corresponding to each UE belonging tothe serving cell are also calculated using the reported OMA CQIs (i.e.,CQI_(UE1) ⁰ and CQI_(UE2) ⁰) as is currently done in LTE.

Step 8:

From Step 7, the scheduler decides whether OMA or MUST should beemployed in the current scheduling band depending on which schemeprovides the highest PF rate. The UE(s) corresponding to the highest PFmetric are scheduled. In case the MUST scheme is scheduled in thescheduling band, the power share parameter pair ({tilde over (α)},α_(q)) that yields the highest PF rate is chosen.

In one variant of this embodiment, the eNodeB, in Step 1, may configurea far UE UE₂ using LTE transmission mode 10 to send a single CSI reportcontaining a CQI while at the same time transmitting the interferenceterm √{square root over (αP)}g_(F)(k)x_(N)(k) (see Equation 9) in UE₂'sinterference measurement resource (IMR). The far UE UE₂ may not be awareof the superposed interference from UE₁ and may not be configured toreceive multi-user superposition transmission. Since transmitting theinterference term on the IMR improves a UE's interference estimatewithout requiring any a-priori knowledge of the interferencecharacteristics, the CSI feedback from a far UE served by multi-usersuperposition transmission can be improved without any additional UEcomplexity. There may be further improvements for the CSI estimate ofthe far UE if the CSI report of UE₂ is configured with a MUST powershare value of (1−α) as well. Note that since the power offset valuesused for CSI in LTE Rel-12 (for example, P_(c) described in furtherdetail below) may cover the range needed for the far UE served by MUSTtransmissions, the far UE may not need to be aware that its power sharevalue of (1−α) is for the purpose of MUST transmission

It should be noted that MUST specific CSI (i.e., CQI_(UE1) ^(q)) is usedin this solution for identifying valid MUST pairs (Step 3), calculatingnear UE's MUST scheduling SINR (Step 5), and computing the MUST PFmetrics (Step 6). As a result, the problems of rank mismatch, CQImismatch, and PMI mismatch are alleviated in this solution. In addition,the solution of Embodiment 1 also supports dynamic switching between OMAand MUST modes. That is, the scheduler in the proposed scheme can moreaccurately decide whether OMA or MUST should be employed in a givenscheduling band depending on which scheme provides the highest PF rate.

The RRC signaling required to support the solution of Embodiment 1 inLTE transmission mode 10, TM10, can be realized in a few different ways.In current LTE, a parameter P_(c) is signaled by the eNodeB to the UE toindicate the ratio of the PDSCH energy per resource element (‘EPRE’) toCSI-RS EPRE. In other words, the P_(c) parameter indicates the ratio ofthe downlink data transmitted power per resource element to the channelstate information reference symbol power per resource element. The UEuses the P_(c) parameter to determine the reference data transmissionpower during CSI feedback. Currently, P_(c) takes values in the range of[−8, 15] dB with 1 dB step size. However, to support the solution ofEmbodiment 1, the range of P_(c) should be extended to cover the desirednear UE power share {tilde over (α)} values in dB. For instance, therange of near UE power share values in Table 1 should be covered. So ifthe range of P_(c) is extended to [−19, 15] dB then all the possibleREMA cases in Table 1 should be covered. However, if extending the rangeof P_(c) value to −19 dB is an overkill, then a more reasonable rangeextension for P_(c) would be [−13, 15] dB which covers a majority ofsuperposed REMA constellations in Table 1.

An example using RRC signaling of the CSI-Process information elementwith the range-extended P_(c) parameter (which is denoted as p-C-r11) isshown in Table 2. With the CSI-Process information element of Table 2,an eNodeB can currently configure a UE to report 2 MUST specific CQIsand 1 OMA CQI (a total of Q=3 CSI reports). This is because in currentLTE it is possible to configure a maximum of 3 CSI-RS processes per UEin TM10 (i.e., the maxCQI-ProcEt-r11 parameter can be currently set to3, for example). However, if maxCQI-ProcExt-r11 is further increased, itis possible to have more than 2 MUST specific CQIs (i.e., Q>3).

Alternatively, if subframe patterns for CSI (CQI/PMI/PTI/RI) reportingare configured (i.e. csi-SubframePatternConfig is configured), then theUE can be configured to send two CSI reports per CSI process in the twoCSI measurement subframe sets currently supported in LTE. In each CSIprocess, two different P_(c) values can be set in the two CSImeasurement subframe sets by having two entries in p-C-AndCBSRList-r11.This can be exploited to configure up to Q=6 CSI reports in LTE TM10(i.e., 2 CSI reports per CSI process×3 CSI processes). Hence, byconfiguring subframe patterns for CSI reporting, it is possible for theeNodeB to configure a near UE to report up to 5 MUST specific CSIs and 1OMA CSI.

Yet another alternative is to introduce a new sequence called p-C-Listin the CSI-Process information element. This sequence will contain aconfigurable number (for instance, say Q) of entries of type P_(c). Inthis alternative, the eNodeB will configure the UE to report Q CSImeasurements from the same CSI process (thus, reducing the CSI-RSoverhead from having to use multiple CSI processes). Each of the Q CSTreports will correspond to one of P_(c) values contained in p-C-List.Thus, with this alternative, Embodiment 1 can be realized in LTE TM10with a flexibly configurable number Q of CSI reports.

TABLE 2 CSI-Process information element -- ASN1START CSI-Process-r11 ::=SEQUENCE { csi-ProcessId-r11 CSI-ProcessId-r11, csi-RS-ConfigNZPId-r11CSI-RS-ConfigNZPId-r11, csi-IM-ConfigId-r11 CSI-IM-ConfigId-r11,p-C-AndCBSRList-r11  SEQUENCE (SIZE (1..2)) OF P-C-AndCBSR-r11,cqi-ReportBothProc-r11 CQI-ReportBothProc-r11 OPTIONAL, -- Need ORcqi-ReportPeriodicProcId-r11 INTEGER (0..maxCQI-ProcExt-r11) OPTIONAL,-- Need OR cqi-ReportAperiodicProc-r11 CQI-ReportAperiodicProc-r11 OPTIONAL, -- Need OR .... [[ alternativeCodebookEnabledFor4TXProc-r12ENUMERATED {true} OPTIONAL, -- Need ON csi-IM-ConfigIdList-r12 CHOICE {release NULL, setup SEQUENCE (SIZE (1..2)) OF CSI-IM-ConfigId- r12 }OPTIONAL, -- Need ON cqi-ReportAperiodicProc2-r12 CHOICE { release NULL,setup CQI-ReportAperiodicProc-r11 } OPTIONAL -- Need ON ]] }P-C-AndCBSR-r11 ::= SEQUENCE { p-C-r11 INTEGER (−13..15),codebookSubsetRestriction-r11 BIT STRING } -- ASN1STOPCSI-Process field descriptions are as follows.alternativeCodebookEnabledFor4TXProc

Indicates whether code book in TS 36.213 Table 7.2.4-0A to Table7.2.4-0D is being used for deriving CSI feedback and reporting for a CSIprocess. EUTRAN may configure the field only if the number of CSI-RSports for non-zero power transmission CSI-RS configuration is 4.

cqi-ReportAperiodicProc

If csi-MeasSubframeSets-r12 is configured for the same frequency as theCSI process, cqi-ReportAperiodicProc

applies for CSI subframe set 1. If csi-MeasSubframeSet1-r10 orcsi-MeasSubframeSet2-r10 are configured for the same frequency as theCSI process, cqi-ReportAperiodicProc applies for CSI subframe set 1 orCSI subframe set 2. Otherwise, cqi-ReportAperiodicProc applies for allsubframes

cqi-ReportAperiodicProc2

cqi-ReportAperiodicProc2 is configured only if csi-MeasSubframeSets-r12is configured for the same frequency as the CSI process.cqi-ReportAperiodicProc2 is for CSI subframe set 2. E-UTRAN shall setcqi-ReportModeAperiodic-r11 in cqi-ReportAperiodicProc2 the same as incqi-ReportAperiodicProc.

cqi-ReportBothProc

Includes CQI configuration parameters applicable for both aperiodic andperiodic CSI reporting, for which CSI process specific values may beconfigured. E-UTRAN configures the field if and only ifcqi-ReportPeriodicProcId is included and/or if cqi-ReportAperiodicProcis included.

cqi-ReportPeriodicProcId

Refers to a periodic CQI reporting configuration that is configured forthe same frequency as the CSI process. Value 0 refers to the set ofparameters defined by the REL-10 CQI reporting configuration fields,while the other values refer to the additional configurations E-UTRANassigns by CQI-ReportPeriodicProcExt-r11 (and as covered byCQI-ReportPeriodicProcExtId).

csi-IM-ConfigId

Refers to a CSI-IM configuration that is configured for the samefrequency as the CSI process.

csi-IM-ConfigIdList

Refers to one or two CSI-IM configurations that are configured for thesame frequency as the CSI process. csi-M-ConfigIdList can include 2entries only if csi-MeasSubframeSets-r12 is configured for the samefrequency as the CSI process. UE shall ignore csi-IM-ConfigId-r11 ifcsi-IM-ConfigIdList-r12 is configured.

csi-RS-ConfigNZPId

Refers to a CSI RS configuration using non-zero power transmission thatis configured for the same frequency as the CSI process.

p-C

Parameter: P_(c), see TS 36.213.

p-C-AndCBSRList

A p-C-AndCBSRList including 2 entries indicates that the subframepatterns configured for CSI (CQI/PMI/PTI/RI) reporting (i.e. as definedby field csi-MeasSubframeSet1 and csi-MeasSubframeSet2, or as defined bycsi-MeasSubframeSets-r12) are to be used for this CSI process, while asingle entry indicates that the subframe patterns are not to be used forthis CSI process. E-UTRAN does not include 2 entries in p-C-AndCBSRListwith csi-MeasSubframeSet1 and csi-MeasSubframeSet2 for CSI processesconcerning a secondary frequency. E-UTRAN includes 2 entries inp-C-AndCBSRList when configuring both cqi-pmi-ConfigIndex andcqi-pmi-ConfigIndex2.

The RRC signaling required to support the solution of Embodiment 1 inLTE transmission mode 9, TM9, can be realized in a few different ways.An example RRC signaling of the CSI-RS-Config information element isshown in Table. Here, a new optional integer p-C2 is introduced in theCSI-RS-Config information element with range [−13, 15] dB which covers amajority of the superposed REMA constellations in Table 1. If subframepatterns for CSI (CQI/PMI/PTI/RI) reporting are configured (i.e.csi-SubframePatternConfig is configured), then the existing integerp-C-r10 is only used in the first CSI-MeasSubframeSet (i.e.,CSI-MeasSubframeSet1) and the newly introduced integer p-C2 is only usedin the second CSI-MeasSubframeSet (i.e., CSI-MeasSubframeSet2). This waythe eNodeB can configure a near UE in TM9 to send one OMA CSI report onthe first CSI-MeasSubframeSet and one MUST CSI report on the secondCSI-MeaSubframeSet. Note that the parameter p-C2 is only signaled if theeNodeB wants to enable multiple CSI reports for the purposes of MUST.Hence, with this RRC signaling approach, the solution of Embodiment 1can be supported in LTE TM9 with Q=2.

An alternative RRC signaling approach is to introduce a new sequencecalled p-C-List in the CSI-RS-Config information element. This sequencewill contain a configurable number (for instance, say Q) of entries oftype P_(c). The range of values for P_(c) will be extended to cover theMUST near UE power share values of interest (for instance, this rangecan be set to [−13, 15] dB as discussed above). In this alternative, theeNodeB will configure the UE to report Q CSI measurements perCSI-RS-Config. Each of the Q CSI reports will correspond to one of Pvalues contained in p-C-List. Thus, with this alternative, Embodiment 1can be realized in LTE TM9 with a flexibly configurable number Q of CSIreports.

TABLE 3 CSI-RS-Config information element -- ASN1START CSI-RS-Config-r10::= SEQUENCE {  csi-RS-r10 CHOICE { release NULL, setup SEQUENCE {antennaPortsCount-r10 ENUMERATED {an1, an2, an4, an8},resourceConfig-r10 INTEGER (0..31), subframeConfig-r10 INTEGER (0..154),p-C-r10 INTEGER (−8..15), p-C2 INTEGER (−13..15) }  } OPTIONAL, -- NeedON  zeroTxPowerCSI-RS-r10 ZeroTxPowerCSI-RS-Conf-r12 OPTIONAL -- Need ON} CSI-RS-Config-v1250 ::= SEQUENCE {  zeroTxPowerCSI-RS2-r12ZeroTxPowerCSI-RS-Conf-r12 OPTIONAL,  -- Need ON ds-ZeroTxPowerCSI-RS-r12 CHOICE { release NULL, setup SEQUENCE {zeroTxPowerCSI-RS-List-r12 SEQUENCE (SIZE (1..maxDS-ZTP-CSI- RS-r12)) OFZeroTxPowerCSI-RS-r12 }  } OPTIONAL -- Need ON }ZeroTxPowerCSI-RS-Conf-r12 ::= CHOICE { release NULL, setupZeroTxPowerCSI-RS-r12 } ZeroTxPowerCSI-RS-r12::= SEQUENCE { zeroTxPowerResourceConfigList-r12 BIT STRING (SIZE (16)), zeroTxPowerSubframeConfig-r12 INTEGER (0..154) } -- ASN1STOPCSI-RS-Config field descriptions will be provided.ds-ZeroTxPowerCSI-RS

Parameter for additional zeroTxPowerCSI-RS for a serving cell,concerning the CSI-RS included in discovery signals.

zeroTxPowerCSI-RS2

Parameter for additional zeroTxPowerCSI-RS for a serving cell. E-UTRANconfigures the field only if csi-MeasSubframeSets-r12 and TM 1-9 areconfigured for the serving cell.

p-C

Parameter: P_(c), see TS 36.213 (See Section 7.2.5).

p-C2

Additional P_(c) parameter (see Section 7.2.5) only signalled whensubframe patterns for CSI (CQI/PMI/PTI/RI) reporting are configured andwhen multiple CQI reports for the purposes of MUST are desired. Ifsignalled, p-C is only used in the first (CSI-MeasSubframeSet (i.e.,CSI-MeasSubframeSet1) and p-C2 is only used in the secondCSI-MeasSubframeSet (i.e., CSI-MeasSubframeSet2).

resourceConfig

Parameter: CSI reference signal configuration, see TS 36.211 (See Tables6.10.5.2-1 and 6.10.5.2-2)

subframeConfig

Parameter: I_(CSI-RS), see TS 36.211 (See Tables 6.10.5.3-1).

zeroTxPowerResourceConfigList

Parameter: ZeroPowerCSI-RS, see TS 36.213 (See Section 7.2.7).

zeroTxPowerSubframeConfig

Parameter: I_(CSI-RS), see TS 36.211 (See Table 6.10.5.3-1).

The RRC signaling required to support the solution of Embodiment 1 inLTE transmission mode 4, TM4, can be realized in a few different ways.In current LTE, a parameter P_(A) is signaled by the eNodeB to the UEwhich is used to define the ratio of the PDSCH EPRE to cell specific RS(‘CRS’) EPRE. In TM4, the UE uses the P_(A) parameter to determine thereference data transmission power during CSI feedback. Currently, P_(A)can take on values of {−6 dB, −4.77 dB, −3 dB, −1.77 dB, 0 dB, 1 dB, 2dB, 3 dB}. However, to support the solution of Embodiment 1, the rangeof P_(A) should be extended to cover the desired near UE power share{tilde over (α)} values in dB. For instance, the range of near UE powershare values in Table 1 should be covered. So if additional values of−19.21 dB, −13.19 dB, −12.29 dB, and −6.9867 dB can be added to the listof possible P_(A) values then all the possible REMA cases in Table 1should be covered. If this is overkill, a subset of these additionalvalues can be added to the list of possible P_(A) values so that most ofthe superposed REMA constellations in Table 1 can be supported.

One alternative is to define a new information element, IE, calledMUST-AssistanceInfo as shown in Table 4. This new IE will be part of thededicated RRC signaling. The IE contains a sequence servCellp-aList ofsize maxP-a-PerServCell-r13 (containing P_(A) values) to be signaledwhen multiple CSI reports for the purposes of MUST are desired. In thisalternative, the eNodeB will configure the UE to report Q CSImeasurements where Q is equal to maxP-a-PerServCell-r13. Each of the QCQIs in the CSI reports will correspond to one of Pa values contained inservCellp-aList. Thus, with this alternative, Embodiment 1 can berealized in LTE TM4 with a flexibly configurable number Q of CSIreports.

In another alternative, the size of servCellp-aList in Table 4 can beset to 2 If subframe patterns for CSI (CQI/PMI/PTI/RI) reporting areconfigured (i.e., csi-SubframePatternConfig is configured), then thefirst P_(A) value in servCellp-aList is only used in the firstCSI-MeasSubframeSet (i.e., CSI-MeasSubframeSet1) and the second P_(A)value in servCellp-aList is only used in the second CSI-MeasSubframeSet(i.e., CSI-MeasSubframeSet2). This way the eNodeB can configure a nearUE in TM4 to send one OMA CSI report on the first CSI-MeasSubframeSetand one MUST CSI report on the second CSI-MeasSubframeSet. Hence, withthis RRC signaling approach, the solution of Embodiment 1 can besupported in LTE TM4 with Q=2.

TABLE 4 MUST-AssistanceInfo information element MUST-AssistanceInfo-r13::= CHOICE {  release NULL,  setup SEQUENCE {  servCellp-aList-r13SEQUENCE (SIZE (1..maxP-a-PerServCell-r13)) OF P-a OPTIONAL -- Need ON } } P-a ::- ENUMERATED { dB-13dot19, dB-6, dB-4dot77, dB-3, dB-1dot77,dB0, dB1, dB2, dB3}MUST-AssitanceInfo field descriptions are defined as the following.P-a

Parameter: P_(A), see TS 36.213 (see Section 5.2). Value dB-6corresponds to −6 dB, dB-4dot77 corresponds to −4.77 dB etc.

servCellp-aList

Indicates the list of P_(A) parameters to be only signalled whenmultiple CSI reports for the purposes of MUST are desired.

Embodiment 2

In this embodiment, the eNodeB generally configures the UE(s) to sendmultiple CSIs for the purposes of MUST wherein each of several CQIsamong the CSI reports corresponds to different rank restrictions. If theeNodeB is equipped with N_(Tx) transmit antennas and each UE has N_(Rx)receive antennas, then the maximum transmission rank possible is givenbyR _(max)=min(N _(Tx) ,N _(Rx)).   Equation 16

Hence, in this embodiment, the eNodeB may configure the UE to reportR_(max) CQIs. For instance, when R_(max)=2, the UE will report 2 CQIswhere the first CQI will be restricted to rank 1 and the second CQI willbe restricted to rank 2. The UE will assume full data transmission poweris allocated to the UE when calculating CSI feedback. Furthermore, theeNodeB can easily determine the OMA CSI by choosing the CSI report withthe CQI that provides the best instantaneous throughput among theR_(max) CSI reports. To reduce uplink feedback overhead, the eNodeB mayconfigure only the near UE(s) to send multiple CQI reports for thepurposes of MUST, the far UE(s) may be configured to send only a singleOMA CSI report. The eNodeB may use RSRP reports and/or uplink pathlossmeasurements to distinguish between the near and far UEs. The stepsinvolved in this embodiment are summarized below. Although these stepsare described using one near UE and one far UE, the solution proposed inthis embodiment is applicable to a plurality of near and far UEs.

Step 1:

The eNodeB configures a near UE UE₁ to send R_(max)>1 CSI reports. Ther^(th) CSI report with CQI_(UE1) ^(r) of UE₁ is restricted to rank rwhere 1≤r≤R_(max). Additionally, the eNodeB configures a far UE UE₂ tosend a single OMA CSI report that contains a CQI denoted by CQI_(UE2).

Step 2:

UE₁ sends the R_(max) CSI reports to the eNodeB. Similarly, UE₂ sendsthe OMA CSI report to the eNodeB. When measuring the R_(max) CSIs, UE₁will assume full data transmission power is allocated to itself.

Step 3:

For each scheduling band, the eNodeB scheduler first determines the OMACSI (containing a CQI denoted by CQI_(UE1)) corresponding to UE₁. Thisis done by choosing the CQI from the CSI reports that provides the bestinstantaneous throughput among CQI_(UE1) ¹, CQI_(UE1) ², . . . ,CQI_(UE1) ^(R) ^(max) .

Step 4:

For each scheduling band, the eNodeB scheduler checks if CQI_(UE1) issufficiently higher than CQI_(UE2). Additionally, the scheduler checksthe combination of precoders among these UEs when deciding whether UE₁and UE₂ can be valid MUST pairs. This is done by comparing the PMIcorresponding to CQI_(UE2) with the PMIs corresponding to CQI_(UE1) ¹,CQI_(UE1) ², . . . , CQI_(UE1) ^(R) ^(max) . If the PMI of CQI_(UE2)matches the PMI of CQI_(UE1) ^(r) where 1≤r≤R_(max), then UE₁ and UE₂can be valid MUST pairs.

Step 5:

If UE₁ and UE₂ are deemed a valid MUST pair, then the eNodeB schedulercan select a near UE power share parameter {tilde over (α)}. Theparameter {tilde over (α)} is selected from a set A of predeterminedpower share parameter values (i.e., {tilde over (α)}∈A).

Step 6:

For the selected C value, calculate the scheduling SINRs for MUST usingSINR_(UE) ₁ and SINR_(UE) ₂ , corresponding to CQI reports CQI_(UE1)^(r) and CQI_(UE2) with the following approximations:

-   -   UE₁'s scheduling SINR for MUST is calculated as        {tilde over (α)}×SINR_(UE1) ^(r)   Equation 17    -   UE₂'s scheduling SINR for MUST is calculated as

$\begin{matrix}\frac{1 - \overset{\sim}{\alpha}}{\overset{\sim}{\alpha} + \frac{1}{{SINR}_{{UE}\; 2}}} & {{Equation}\mspace{14mu} 18}\end{matrix}$

Step 7:

The scheduler then calculates the MUST PF metric corresponding to theMUST UE pair under consideration as

$\begin{matrix}{\sum\limits_{{UE}_{i} \in U}\left( \frac{R\left( {\left. i \middle| U \right.,\overset{\sim}{\alpha}} \right)}{L(i)} \right)} & {{Equation}\mspace{14mu} 19}\end{matrix}$

where R(i|U, {tilde over (α)}) and L(i) respectively denote theinstantaneous throughput and the average throughput of UE_(i). InEquation 19, R(i|U, {tilde over (α)}) is a function of MUST schedulingSINRs computed in Equation 17-Equation 18, and hence R(i|U, {tilde over(α)}) also depends on the power share parameters {tilde over (α)}. Thecandidate user set U contains the MUST UE pair under consideration.

Step 8:

The steps 3-7 are repeated for all valid MUST UE pairs with all rank(i.e., all r) values that yield matching PMIs and all {tilde over (α)}values in the set A. Additionally, the OMA PF metrics corresponding toeach UE belonging to the serving cell are also calculated using thereported OMA CQIs (i.e., CQI_(UE1) and CQI_(UE2)) as is currently donein LTE.

Step 9:

From Step 8, the scheduler decides whether OMA or MUST should beemployed in the current scheduling band depending on which schemeprovides the highest PF rate. The UE(s) corresponding to the highest PFmetric are scheduled. In case the MUST scheme is scheduled in thescheduling band, the power share parameter {tilde over (α)} and the rankvalue r that yield the highest PF rate are chosen.

It should be noted that since the best CQI corresponding to all possibleranks (i.e., all r) are taken into account in this embodiment, theproblems of rank mismatch, CQI mismatch, and PMI mismatch arealleviated. In addition, the solution of Embodiment 2 also supportsdynamic switching between OMA and MUST modes. That is, the scheduler inthe proposed scheme can more accurately decide whether OMA or MUSTshould be employed in a given scheduling band depending on which schemeprovides the highest PF rate. If very high ranks are unlikely due to thechannel conditions, this embodiment can also be used with a rankR<R_(max).

The RRC signaling required to support the solution of Embodiment 2 inLTE TM10 can be realized in a few different ways. In current LTE, aparameter codebookSubsetRestriction is signaled by the eNodeB to the UEto indicate the restricted set of precoders to be considered during CSImeasurements/feedback. The eNodeB could use this parameter to implementdifferent rank restrictions of Embodiment 2 on different CSI reports.

The existing RRC signaling of the CSI-Process information element isshown in Table 5. With the CSI-Process information element of Table 5,an eNodeB can currently configure a UE to send up to R_(max)=3 CSIreports each with different rank restrictions. This is because incurrent LTE it is possible to configure a maximum of 3 CSI-RS processesper UE in TM10 (i.e., the maxCQI-ProcExt-r11 parameter can currently beset to 3, for example). However, if maxCQI-ProcExt-r11 is furtherincreased, it is possible to have more than 3 rank restricted CSIreports (i.e., R_(max)>3).

Alternatively, if subframe patterns for CSI (CQI/PMI/PTI/RI) reportingare configured (i.e. csi-SubframePatternConfig is configured), then theUE can be configured to send two CSI reports per CSI process in the twoCSI measurement subframe sets currently supported in LTE. (Note that PTIstands for precoding type indicator.) In each CSI process, two differentrank restrictions can be set in the two CSI measurement subframe sets byhaving two entries in p-C-AndCBSRList-r11 with appropriatecodebookSubsetRestriction bit strings. This can be exploited toconfigure up to R_(max)=6 CSI reports in LTE TM10 (i.e., 2 CQI reportsper CSI process×3 CSI processes). Hence, by configuring subframepatterns for CSI reporting, it is possible for the eNodeB to configure anear UE to send up to 6 rank restricted CSI reports.

Yet another alternative is to introduce a new sequence called CBSR-Listin the CSI-Process information element. This sequence will contain aconfigurable number (for instance, say R_(max)) of entries of typecodebookSubsetRestriction. In this alternative, the eNodeB willconfigure the UE to report R_(max) CSI measurements from the same CSIprocess (thus, reducing the CSI-RS overhead from having to use multipleCSI processes). Each of the R_(max) CSI reports will correspond to adifferent rank restriction indicated by one of thecodebookSubsetRestriction bit strings contained in CBSR-List. Thus, withthis alternative, Embodiment 2 can be realized in LTE TM10 with aflexibly configurable number R_(max) of CSI reports.

TABLE 5 CSI-Process information elements -- ASN1START CSI-Process-r11::= SEQUENCE {  csi-ProcessId-r11 CSI-ProcessId-r11, csi-RS-ConfigNZPId-r11 CSI-RS-ConfigNZPId-r11,  csi-IM-ConfigId-r11CSI-IM-ConfigId-r11,  p-C-AndCBSRList-r11 SEQUENCE (SIZE (1..2)) OFP-C-AndCBSR-r11,  cqi-ReportBothProc-r11 CQI-ReportBothProc-r11OPTIONAL, -- Need OR  cqi-ReportPeriodicProcId-r11 INTEGER(0..maxCQI-ProcExt-r11)  OPTIONAL, -- Need OR cqi-ReportAperiodicProc-r11 CQI-ReportAperiodicProc-r11 OPTIONAL, --Need OR  ...,  [[ alternativeCodebookEnabledFor4TXProc-r12 ENUMERATED{true}  OPTIONAL, -- Need ON csi-IM-ConfigIdList-r12 CHOICE { releaseNULL, setup SEQUENCE (SIZE (1..2)) OF CSI-IM-ConfigId- r12 } OPTIONAL,-- Need ON cqi-ReportAperiodicProc2-r12 CHOICE { release NULL setupCQI-ReportAperiodicProc-r11 } OPTIONAL -- Need ON  ]] } P-C-AndCBSR-r11::= SEQUENCE {  p-C-r11 INTEGER (−8..15),  codebookSubsetRestriction-r11BIT STRING } -- ASN1STOPCSI-Process field descriptions are described above.

The RRC signaling required to support the solution of Embodiment 2 inLTE TM4 and TM9 can be realized in a few different ways. One alternativeis to define a new IE called MUST-AssistanceInfo as shown in Table 6.This new IE will be part of the dedicated RRC signaling. The IE containsa sequence CBSRList of size maxCBSR-r13 (containingcodebookSubsetRestriction values) to be signaled when multiple CSIreports for the purposes of MUST are desired. In this alternative, theeNodeB will configure the UE to report R_(max) CSI measurements whereR_(max) is equal to maxCBSR-r13. Each of the R_(max) CSI reports willcorrespond to a different rank restriction indicated by one of thecodebookSubsetRestriction bit strings contained in CBSRList. Thus, withthis alternative, Embodiment 2 can be realized in LTE TM4 and TM9 with aflexibly configurable number R_(max) of CSI reports.

In another alternative, the size of CBSRList in Table 6 can be set to 2.If subframe patterns for CSI (CQI/PMI/PTI/RI) reporting are configured(i.e. csi-SubframePatternConfig is configured), then the rankrestriction indicated by the first codebookSubsetRestriction bit stringin CBSRList is only used in the first CSI-MeasSubframeSet (i.e.,CSI-MeasSubframeSet1) and the rank restriction indicated by the secondcodebookSubsetRestriction bit string in CBSRList is only used in thesecond CSI-MeasSubframeSet (i.e., CSI-MeasSubframeSet2). This way theeNodeB can configure a near UE in TM4 or TM9 to report one rank-1 CQI onthe first CSI-MeasSubframeSet and one rank-2 CQI on the secondCSI-MeasSubframeSet. Hence, with this RRC signaling approach, thesolution of Embodiment 2 can be supported in LTE TM4 and TM9 withR_(max)=2.

TABLE 6 MUST-AssistanceInfo information element MUST-AssistanceInfo-r13::= CHOICE {  release NULL,  setup SEQUENCE {  CBSRList-r13 SEQUENCE(SIZE(1..maxCBSR-r13)) OF codebookSubsetRestriction OPTIONAL -- Need ON } } codebookSubsetRestriction BIT STRING OPTIONALMUST-AssistanceInfo field descriptions are described as follows.codebookSubsetRestriction

-   -   Parameter: codebookSubsetRestriction, see TS 36.213 (see Section        7.2) and TS 36.211 (see Section 6.3.4.2.3). The number of bits        in the codebookSubsetRestriction for applicable transmission        modes is defined in TS 36.213 (see Table 7.2-1b). If the UE is        configured with transmission lode tm8, E-UTRAN configures the        field codebookSubsetRestriction if PMI/RI reporting is        configured. If the UE is configured with transmissionMode tm9,        E-UTRAN configures the field codebookSubsetRestriction if PMI/RI        reporting is configured and if the number of CSI-RS ports is        greater than 1. E-UTRAN does not configure the field        codebookSubsetRestriction in other cases where the UE is        configured with transmissionMode tm8 or tm9.        servCellp-aList    -   Indicates the list of codebookSubsetRestriction parameters to be        only signalled when multiple CSI reports for the purposes of        MUST are desired.

In some cases, it may be desirable to configure the UE so that itprovides a mixed-rank CSI in addition to one or more rank-restrictedCSIs, particularly when the maximum supportable rank is high. Forinstance, if there are there three CST processes and up to four ranks,then the UE might be configured, using the above techniques, to report arank-1 CSI for the first CSI process, a rank-2 CSI for the second CSIprocess, and a joint rank3-rank4 restriction on the third process(meaning that the third CSI process can consider both rank-3 andrank-4). This way embodiment 2 can be supported for higher rank caseswithout increasing the number of CSI processes.

Embodiment 3

In this embodiment, the eNodeB configures the UE(s) to send Z>1 CSIreports for the purposes of MUST wherein the z^(th) CSI report containsthe z^(th) best CQI (the corresponding PMI and RI are also included inthe report). The UE will assume full data transmission power isallocated to the UE during CSI measurement corresponding to all CSIreports. To reduce uplink feedback overhead, the eNodeB may configureonly the near UE(s) to send multiple CSI reports for the purposes ofMUST; the far UE(s) may be configured to send only a single OMA CSIreport. The eNodeB may use RSRP reports and/or uplink pathlossmeasurements to distinguish between the near and far UEs The stepsinvolved in this embodiment are summarized below. Although these stepsare described using one near UE and one far UE, the solution proposed inthis embodiment is applicable to a plurality of near and far UEs.

Step 1:

The eNodeB configures a near UE UE₁ to send Z>1 CSI reports. One of theCQIs in the reports denoted by CQI_(UE1) ⁰ corresponds to the OMA CQI(i.e., the best CQI). The remaining Z−1 CQIs in the reports are denotedby CQI_(UE1) ¹, CQI_(UE1) ², . . . , CQI_(UE1) ^(Z−1), where the z^(th)CSI report with CQI_(UE1) ^(z) contains the z^(th) best CQI.Additionally, the eNodeB configures a far UE UE₂ to report a single OMACSI report that contains a CQI that is denoted by CQI_(UE2) ⁰.

Step 2:

UE₁ sends the Z CSI reports to the eNodeB. Similarly, UE₂ sends the OMACSI report to the eNodeB. When measuring the Z CSIs, UE₁ will assumefull data transmission power is allocated to itself.

Step 3:

For each scheduling band, the eNodeB scheduler first checks if CQI_(UE1)⁰ is sufficiently higher than CQI_(UE2) ⁰. Additionally, the schedulerchecks the combination of precoders among these UEs when decidingwhether UE₁ and UE₂ can be valid MUST pairs. This is done by comparingthe PMI corresponding to CQI_(UE2) ⁰ with the PMIs corresponding toCQI_(UE1) ⁰, CQI_(UE1) ², . . . , CQI_(UE1) ^(Z−1). If the PMI ofCQI_(UE2) ⁰ matches the PMI of CQI_(UE1) ^(z) where 0≤z≤(Z−1), then UE₁and UE₂ can be valid MUST pairs.

Step 4:

If UE₁ and UE₂ are deemed a valid MUST pair, then the eNodeB schedulercan select a near UE power share parameter {tilde over (α)}. Theparameter {tilde over (α)} is selected from a set A of predeterminedpower share parameter values (i.e., {tilde over (α)}∈A).

Step 5:

For the selected {tilde over (α)} value, calculate the scheduling SINRsfor MUST using SINR_(UE) ₁ and SINR_(UE) ₂ , corresponding to CQIreports CQI_(UE1) ^(z) and CQI_(UE2) ⁰ with the followingapproximations:

-   -   UE₁'s scheduling SINR for MUST is calculated as        {tilde over (α)}×SINR_(UE1) ^(z)   Equation 20    -   UE₂'s scheduling SINR for MUST is calculated as

$\begin{matrix}\frac{1 - \overset{\sim}{\alpha}}{\overset{\sim}{\alpha} + \frac{1}{{SINR}_{{UE}\; 2}^{0}}} & {{Equation}\mspace{14mu} 21}\end{matrix}$

Step 6:

The scheduler then calculates the MUST PF metric corresponding to theMUST UE pair under consideration as

$\begin{matrix}{\sum\limits_{{UE}_{i} \in U}\left( \frac{R\left( {\left. i \middle| U \right.,\overset{\sim}{\alpha}} \right)}{L(i)} \right)} & {{Equation}\mspace{14mu} 22}\end{matrix}$

where R(i|U, {tilde over (α)}) and L(i) respectively denote theinstantaneous throughput and the average throughput of UE_(i). InEquation 22, R(i|U, {tilde over (α)}) is a function of MUST schedulingSINRs computed in Equation 20-Equation 21, and hence R(i|U, {tilde over(α)}) also depends on the power share parameter {tilde over (α)}. Thecandidate user set U contains the MUST UE pair under consideration.

Step 7:

The steps 3-6 are repeated for all valid MUST UE pairs with all possiblez values that yield matching PMIs and all {tilde over (α)} values in theset A. Additionally, the OMA PF metrics corresponding to each UEbelonging to the serving cell are also calculated using the reported OMACQIs (i.e., CQI_(UE1) ⁰ and CQI_(UE2) ⁰) as is currently done in LTE.

Step 8:

From Step 7, the scheduler decides whether OMA or MUST should beemployed in the current scheduling band depending on which schemeprovides the highest PF rate. The UE(s) corresponding to the highest PFmetric are scheduled. In case the MUST scheme is scheduled in thescheduling band, the power share parameter {tilde over (α)} and the zvalue that yield the highest PF rate are chosen.

It should be noted that since Z best CQIs corresponding to the near UEare taken into account in this embodiment, the problems of rankmismatch, CQI mismatch, and PMI mismatch are alleviated. In addition,the solution of Embodiment 3 also supports dynamic switching between OMAand MUST modes. That is, the scheduler in the proposed scheme can moreaccurately decide whether OMA or MUST should be employed in a givenscheduling band depending on which scheme provides the highest PF rate.

Aperiodic CSI Feedback for MUST Transmission

Reporting multiple RI/PMI/CQIs periodically for a UE means increaseduplink feedback overhead. One solution to reduce the feedback overheadis to only feedback/report the multiple configured RI/PMI/CQI whenrequested. In other words, a UE only reports multiple RI/PMI/CQIs whenit is requested by the serving eNodeB or a network node. The request canbe dynamically indicated to the UE by the eNodeB. A UE may be configuredwith one RI/PMI/CQI hypothesis assuming full transmit power (existingLTE CQI configuration) and with additional RI/PMI/CQI hypothesis asdiscussed in the previous embodiments using RRC signaling. A UE onlyreport a new RI/PMI/CQI based on one of the additional hypothesis whenrequested by the eNodeB as shown in FIG. 6. The request can be triggeredin a subframe by subframe basis. For example, when a potential UE pairis identified for MUST transmission, the eNodeB may send a request tothe near UE for a CQI report based on a reduced transmit power to getbetter CQI (and/or RI) estimation for MUST transmission.

Since the CQI mismatch during MUST scheduling mainly occurs to near UEswith large transmit power reduction (i.e., the UEs that feedback higherrank CSI when assuming full transmit power allocation), the requestsfrom the eNodeB may only be sent to near UEs and the feedback may berestricted to rank 1 PMI/CQI reports.

FIG. 7 illustrates a diagram of a radio access network node 30, such asa base station or a base station operating in coordination with a basestation controller, according to some embodiments. The radio accessnetwork node 30 includes one or more communication interface circuits 38in order to communicate with network nodes or peer nodes. The radioaccess network node 30 provides an air interface to wireless devices,which is implemented via one or more antennas 34 and a transceivercircuit 36. The transceiver circuit 36 may include transmitter circuits,receiver circuits, and associated control circuits that are collectivelyconfigured to transmit and receive signals according to a radio accesstechnology for the purposes of providing communication services.According to various embodiments, the radio access network node 30 cancommunicate with one or more peer nodes or core network nodes. Thetransceiver circuit 36 is configured to communicate using cellularcommunication services operated according to wireless communicationstandards (e.g. Global System for Mobile communication (GSM), GeneralPacket Radio Services (GPRS), Wideband Code Division Multiple Access(WCDMA), High Speed Downlink Packet Access (HSDPA), LTE andLTE-Advanced).

The radio access network node 30 also includes one or more processingcircuits 32 that are operatively associated with the communicationinterface circuit(s) 38 and/or the transceiver circuit 36. Theprocessing circuit 32 comprises one or more digital processors 42, e.g.,one or more microprocessors, microcontrollers, Digital Signal Processorsor DSPs, Field Programmable Gate Arrays or FPGAs, Complex ProgrammableLogic Devices or CPLDs, Application Specific Integrated Circuits orASICs, or any combination thereof. More generally, the processingcircuit 32 may comprise fixed circuitry, or programmable circuitry thatis specially configured via the execution of program instructionsimplementing the functionality taught herein, or may comprise somecombination of fixed and programmable circuitry. The processor(s) 42 maybe multi-core.

The processing circuit 32 also includes a memory 44. The memory 44, insome embodiments, stores one or more computer programs 46 and,optionally, configuration data 48. The memory 44 provides non-transitorystorage for the computer program 46 and it may comprise one or moretypes of computer-readable media, such as disk storage, solid-statememory storage, or any combination thereof. By way of non-limitingexample, the memory 44 may comprise any one or more of StaticRandom-Access Memory (SRAM), Dynamic Random-Access Memory (DRAM),Electrically Erasable Programmable Read-Only Memory (EEPROM), and FLASHmemory, which may be in the processing circuit 32 and/or separate fromthe processing circuit 32. In general, the memory 44 comprises one ormore types of computer-readable storage media providing non-transitorystorage of the computer program 46 and any configuration data 48 used bythe node 30.

The radio access network node 30 is configured to support thetransmission of multi-user superposition transmissions, where multi-usersuperposition transmission comprises transmitting, in each of aplurality of time-frequency resource elements, a modulation symbolintended for a first UE and a modulation symbol intended for a secondUE, using the same antennas and the same antenna precoding. Theprocessing circuit 32 is configured to receive multiple CSI reports fromthe first UE for a first reporting instance, wherein one or more of thereceived multiple CSI reports correspond to different possiblemulti-user superposition transmission states. The processing circuit 32is configured to determine whether to use multi-user superpositiontransmission or an orthogonal multiple access transmission forscheduling the first UE in a first scheduling interval, based on thereceived multiple CSI reports. Furthermore, the processing circuit 32 isconfigured to perform any of the operations described in the embodimentsabove for the radio access network node. This functionality may berepresented or carried out by scheduling circuitry 40.

Regardless of the implementation, the processing circuit 32 isconfigured to perform operations, as described in the above embodiments.For example, the processing circuit 32 is configured to perform method800 illustrated by the flowchart in FIG. 8. The method 800 operates in aradio access network node 30 configured to support the transmission ofmulti-user superposition transmissions, where multi-user superpositiontransmission comprises transmitting, in each of a plurality oftime-frequency resource elements, a modulation symbol intended for afirst LIE and a modulation symbol intended for a second UE, using thesame antennas and the same antenna precoding. The method 800 includesreceiving multiple CSI reports from the first UE for a first reportinginstance, wherein one or more of the received multiple CSI reportscorrespond to different possible multi-user superposition transmissionstates (block 802). The method 800 also includes determining whether touse multi-user superposition transmission or an orthogonal multipleaccess transmission for scheduling the first UE in a first schedulinginterval, based on the received multiple CSI reports (block 804).

In some cases, the first UE is sent scheduling messages or configurationmessages, the configuration messages directing the first UE to providemultiple CSI reports for at least the first reporting instance.

A first one of the received multiple CSI reports may include a CQIcorresponding to a full-power or substantially full-power datatransmission to the first UE. Note that “first” does not limit theembodiment or the claims to any type of order or sequence of receivingCQI reports.

The radio access network node 30 then determines whether to usemulti-user superposition transmission or an orthogonal multiple accesstransmission. According to some embodiments, this determination is madeby obtaining a CSI report from a second UE, the CSI report from thesecond UE comprising a CQI corresponding to a full-power orsubstantially full-power data transmission to the second UE, determiningthat multi-user superposition transmission to the first and second UEsis feasible, in that transmission to both UEs can be performed using thesame antennas and antenna precoding and with a power allocation suchthat the signal can be successfully received and decoded by both UEs.

This feasibility determination is made by determining that said CQI forthe first UE is greater than said CQI for the second UE by apredetermined factor or threshold, and determining that a precodermatrix indicator, PMI, corresponding to the CSI report from the secondUE matches at least one PMI corresponding to one of the receivedmultiple CSI reports from the first UE other than said first one of thereceived multiple CST reports.

Obtaining the CSI report from the second UE may include transmitting, inan interference measurement resource, IMR, for the second UE, aninterference component corresponding to a potential power shareallocated to the first UE in a multi-user superposition transmission tothe first and second UEs. The interference component is transmittedusing the same antennas and the same antenna preceding intended for themulti-user superposition transmission to the first and second UEs. Anantenna preceding is as a mapping of one or more signals to multipleantennas, according to preceding weights. Obtaining the CSI report mayfurther include receiving, from the second UE, the CQI corresponding toa full-power or substantially full-power data transmission to the secondUE, wherein said CQI reflects the interference component transmitted inthe IMR for the second UE.

The multiple CSI reports may correspond to different power-sharinghypotheses for multi-user superposition transmission to the first UE,and/or different ranks for data transmission to the first UE. Likewise,configuration messages may indicate different power-sharing hypotheses,and/or a number of CQIs to be reported by the first UE, each CQIcorresponding to a different rank for data transmission to the first UE.In further instances, the configuration messages may signal, for eachdesired CSI report, a corresponding transmission rank by indicating aset of precoders that are restricted to the corresponding transmissionrank. Restricted precoders can mean that a precoder is for use with onlyone rank. Thus, if three indicated precoders are all rank-1 precoders,then it can be inferred by the UE that a CSI is wanted that is specificto rank 1. Likewise, if three indicated precoders are all rank-2precoders, then the UE knows that a CSI specific to rank 2 is desired.

In some cases, it may be desirable to configure the UE so that itprovides a mixed-rank CSI in addition to one or more rank-restrictedCSIs, particularly when the maximum supportable rank is high. Forinstance, if there are there three CSI processes and up to four ranks,then the UE might be configured, using the above techniques, to report arank-1 CSI for the first CSI process, a rank-2 CSI for the second CSIprocess, and a joint rank3-rank4 restriction on the third process.

In some embodiments, the multiple CSI reports from the first UE may alsoinclude N CSI reports, the N CSI reports comprising the N best channelquality indicators, CQIs, and wherein each of the N CSI reports includesa corresponding precoding matrix indicator, PMI, and rank indicator, RI.In some cases, signaling may indicate whether one or more of the CSIreports are for Coordinated MultiPoint, CoMP, transmissions and/or MUSTtransmissions.

FIG. 9 illustrates a diagram of a wireless device, such as UE 50,according to some embodiments. To ease explanation, the user equipment50 may also be considered to represent any wireless devices that mayoperate in a network. The UE 50 herein can be any type of wirelessdevice capable of communicating with a network node or another UE overradio signals. The UE 50 may also be radio communication device, targetdevice, device to device-(D2D), UE, machine type UE or UE capable ofmachine to machine communication (M2M), a sensor equipped with UE,personal digital assistant (PDA), Tablet, mobile terminal, smart phone,laptop embedded equipped (LEE), laptop mounted equipment (LME),Universal Serial Bus (USB) dongles, Customer Premises Equipment (CPE),etc.

The UE 50 communicates with a radio node or base station, such as theradio access network node 30, via antennas 54 and a transceiver circuit56. The transceiver circuit 56 may include transmitter circuits,receiver circuits, and associated control circuits that are collectivelyconfigured to transmit and receive signals according to a radio accesstechnology, for the purposes of providing cellular communicationservices.

The UE 50 also includes one or more processing circuits 52 that areoperatively associated with the transceiver circuit 56. The processingcircuit 52 comprises one or more digital processing circuits, e.g., oneor more microprocessors, microcontrollers, Digital Signal Processors orDSPs, Field Programmable Gate Arrays or FPGAs, Complex ProgrammableLogic Devices or CPLDs, Application Specific Integrated Circuits orASICs, or any mix thereof. More generally, the processing circuit 52 maycomprise fixed circuitry, or programmable circuitry that is speciallyadapted via the execution of program instructions implementing thefunctionality taught herein, or may comprise some mix of fixed andprogrammed circuitry. The processing circuit 52 may be multi-core.

The processing circuit 52 also includes a memory 64. The memory 64, insome embodiments, stores one or more computer programs 66 and,optionally, configuration data 68. The memory 64 provides non-transitorystorage for the computer program 66 and it may comprise one or moretypes of computer-readable media, such as disk storage, solid-statememory storage, or any mix thereof. By way of non-limiting example, thememory 64 comprises any one or more of SRAM, DRAM, EEPROM, and FLASHmemory, which may be in the processing circuit 52 and/or separate fromprocessing circuit 52. In general, the memory 64 comprises one or moretypes of computer-readable storage media providing non-transitorystorage of the computer program 66 and any configuration data 68 used bythe user equipment 50.

The UE 50 is configured to perform at least the modulation anddemodulation techniques described above. For example, the processor 62of the processing circuit 52 may execute a computer program 66 stored inthe memory 64 that configures the processor 62 to operate as a first UE50 configured to support the transmission of multi-user superpositiontransmissions, where multi-user superposition transmission comprisestransmitting, in each of a plurality of time-frequency resourceelements, a modulation symbol intended for the first UE 50 and amodulation symbol intended for a second UE, using the same antennas andthe same antenna precoding. The processing circuit 52 is configured tosend multiple CSI reports for a first reporting instance, wherein one ormore of the received multiple CSI reports correspond to differentpossible multi-user superposition transmission states. Furthermore, theprocessing circuit 52 is configured to perform any of the operationsdescribed in the embodiments above for the UE. Such functionality isrepresented by or carried out by reporting circuitry 60.

The processing circuit 52 of the UE 50 is configured to perform amethod, such as method 1000 of FIG. 10. The method 1000 operates in afirst UE, such as the UE 50, that is configured to support thetransmission of multi-user superposition transmissions, where multi-usersuperposition transmission comprises transmitting, in each of aplurality of time-frequency resource elements, a modulation symbolintended for the first UE 50 and a modulation symbol intended for asecond UE, using the same antennas and the same antenna precoding. Themethod 1000 includes sending multiple CSI reports for a first reportinginstance, wherein one or more of the received multiple CSI reportscorrespond to different possible multi-user superposition transmissionstates (block 1002).

FIG. 11 illustrates an example functional module or circuit architectureas may be implemented in the radio access network node 30, e.g., basedon the scheduling circuitry 40. The illustrated embodiment at leastfunctionally includes a receiving module 1102 for receiving multiple CSIreports from the first UE for a first reporting instance, wherein one ormore of the received multiple CST reports correspond to differentpossible multi-user superposition transmission states. Theimplementation also includes a determining module 1104 for determiningwhether to use multi-user superposition transmission or an orthogonalmultiple access transmission for scheduling the first UE in a firstscheduling interval, based on the received multiple CSI reports.

The scheduling circuitry 40 also includes a configuration module 1106for sending one or more configuration messages, via the transceivercircuit 36, to the first UE. In some embodiments, the one or moreconfiguration messages direct the first UE to provide multiple CSIreports for at least the first reporting instance such that one or moreof the multiple CSI reports correspond to different possible multi-usersuperposition transmission states for a transmission to the first UE.The scheduling circuitry still further includes a scheduling module 1108for scheduling the first UE, based on the determination of whether touse multi-user superposition transmission or an orthogonal multipleaccess transmission. The scheduling module 1108 thus sends a schedulingmessage, via the transceiver circuit 36, to the first UE.

FIG. 12 illustrates an example functional module or circuit architectureas may be implemented in UE 50, e.g., based on the reporting circuitry60. The illustrated embodiment at least functionally includes a sendingmodule 1202 for sending multiple CSI reports for a first reportinginstance, wherein one or more of the received multiple CSI reportscorrespond to different possible multi-user superposition transmissionstates. The illustrated embodiment further comprises a configurationmodule 1204, which in some embodiments is for receiving one or moreconfiguration messages, the one or more configuration messages directingthe first UE to provide multiple CST reports for at least the firstreporting instance such that one or more of the multiple CSI reportscorrespond to different possible multi-user superposition transmissionstates for a transmission to the first UE. The illustrated embodimentstill further comprise a receiving module 1206 for receiving ascheduling message based on the sent multiple CSI reports, thescheduling message scheduling a multi-user superposition transmission tothe first UE.

As described in detail above, multiple CSI reports are used in variousembodiments of the disclosed techniques and apparatus for identifyingvalid MUST pairs, calculating near UE's MUST scheduling SINR, andcomputing the MUST proportional fair scheduling metrics. As a result,the problems of rank mismatch, CQI mismatch, and PMI mismatch arealleviated in this solution. In addition, the proposed solution alsosupports dynamic switching between OMA and MUST modes. Additionally,some embodiments of the proposed solution can be implemented in an LTEstandard transparent manner.

In additional or alternative embodiments, a single CSI report is alsoconceivable, for example in form of a method, in a radio access networknode configured to support the transmission of multi-user superpositiontransmissions, where multi-user superposition transmission comprisestransmitting, in each of a plurality of time-frequency resourceelements, a modulation symbol intended for a first user equipment, UE,and a second modulation symbol intended for a second UE, using the sameantennas and the same antenna precoding. The method comprises receivinga CSI report from the first UE, wherein the received CSI report assumesa transmission power for a physical channel, the transmission powerbeing lower than a minimum transmission power that is assumed whenmulti-user superposition transmission is not used.

FIG. 13 illustrates a process flow 1300 according to this additional oralternative embodiment. As shown at block 1304, the illustrated methodcomprises receiving a CSI report from the first UE, the received CSIreport being based on an assumption that a transmission power for aphysical channel is lower than a minimum transmission power that isassumed when multi-user superposition transmission is not used. As shownat block 1306, the method further comprises transmitting a multi-usersuperposition transmission to the UE, where the transmitting is based onthe received CSI report. As discussed above, CSI reporting according tothe techniques described herein may be facilitated by providing for anextended range for one or more parameters provided to the UE inconfiguration messages, where the range is extended compared toconventional signaling ranges. Thus, some embodiments of the methodshown in FIG. 13 comprise configuring the UE to send the CSI report,where said configuring comprises signaling a selected parameterindicating a ratio of a PDSCH energy per resource element to a CSIreference symbol (CSI-RS) energy per resource element, wherein theselected parameter is selected from a range having a minimum valuecorresponding to a ratio below −8 dB, e.g., somewhere between −8 dB and−19 dB, such as −13 dB. Alternatively or additionally, the configuringmay comprise signaling a selected parameter indicating a ratio of aPDSCH energy per resource element to a cell-specific reference symbol(CRS) energy per resource element, where the selected parameter isselected from an extended range having a minimum value corresponding toa ratio below −6 dB, e.g., corresponding to a ratio of about −19.21 dB.This configuration step is illustrated at block 1302 of FIG. 13.

It will be appreciated that the method shown in FIG. 13 may be carriedout by the radio access network node 30 illustrated in FIGS. 7 and 11,for example, and more specifically using at least the transceivercircuit 36, receiving module 1102, and configuration module 1106.

FIG. 14 illustrates a corresponding method 1400 as implemented in a UEconfigured to support the transmission of multi-user superpositiontransmissions. As shown at block 1402, the illustrated method comprisesreceiving one or more configuration messages from a radio access networknode, the one or more configuration messages directing the UE totransmit a CSI report. These one or more configuration messages compriseat least one of (a) a selected parameter indicating a ratio of a PDSCHenergy per resource element to a CSI-RS energy per resource element,where the selected parameter is selected from a range having a minimumvalue corresponding to a ratio below −8 dB, such as somewhere between −8dB and −19 dB or (b) a selected parameter indicating a ratio of a PDSCHenergy per resource element to a CRS energy per resource element, wherethe selected parameter is selected from an extended range having aminimum value corresponding to a ratio below −6 dB, e.g., about −19.2dB.

The illustrated method further comprises transmitting a CSI report, inaccordance with the one or more configuration messages, as shown atblock 1404, and receiving a multi-user superposition transmission fromthe radio access network node, as shown at block 1406. Once again, itwill be appreciated that the method shown in FIG. 14 may be carried outby the UE 50 illustrated in FIGS. 9 and 12, for example, and morespecifically using at least the transceiver circuit 56, receiving module1206, and configuration module 1204.

Notably, modifications and other embodiments of the disclosedinvention(s) will come to mind to one skilled in the art having thebenefit of the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that theinvention(s) is/are not to be limited to the specific embodimentsdisclosed and that modifications and other embodiments are intended tobe included within the scope of this disclosure. Although specific termsmay be employed herein, they are used in a generic and descriptive senseonly and not for purposes of limitation.

What is claimed is:
 1. A method, in a radio access network nodeconfigured to support the transmission of multi-user superpositiontransmissions, where multi-user superposition transmission comprisestransmitting, in each of a plurality of time-frequency resourceelements, a modulation symbol intended for a first user equipment (UE)and a modulation symbol intended for a second UE, using the sameantennas and the same antenna precoding, the method comprising:receiving multiple channel-state information (CSI) reports from thefirst UE for a first reporting instance, wherein one or more of thereceived multiple CSI reports correspond to one or more respectivemulti-user superposition transmission states; and determining whether touse multi-user superposition transmission or an orthogonal multipleaccess transmission for scheduling the first UE in a first schedulinginterval, based on the received multiple CSI reports.
 2. A method, in afirst user equipment (UE) configured to support the transmission ofmulti-user superposition transmissions, where multi-user superpositiontransmission comprises transmitting, in each of a plurality oftime-frequency resource elements, a modulation symbol intended for thefirst UE and a modulation symbol intended for a second UE, using thesame antennas and the same antenna precoding, the method comprising:receiving one or more configuration messages, the one or moreconfiguration messages indicating number of channel quality indicators(CQIs) to be reported by the first UE, each CQI corresponding to adifferent rank for data transmission to the first UE; and sendingmultiple CSI reports for a first reporting instance, wherein one or moreof the transmitted multiple CSI reports correspond to one or morerespective multi-user superposition transmission states.
 3. A radioaccess network node configured to support the transmission of multi-usersuperposition transmissions, where multi-user superposition transmissioncomprises transmitting, in each of a plurality of time-frequencyresource elements, a modulation symbol intended for a first userequipment (UE) and a modulation symbol intended for a second UE, usingthe same antennas and the same antenna precoding, the radio accessnetwork node comprising: a transceiver circuit configured to send andreceive transmissions; and a processing circuit configured to: receive achannel-state information (CSI) report from the first UE, via thetransceiver circuit, the received CSI report being based on anassumption that a transmission power for a physical channel is lowerthan a minimum transmission power that is assumed when multi-usersuperposition transmission is not used; and control the transceivercircuit to transmit a multi-user superposition transmission to the UE,based on the received CSI report.
 4. The radio access network node ofclaim 3, wherein the processing circuit is configured to use thetransceiver circuit to signal to the UE, for configuring the UE to sendthe CSI report, a selected parameter indicating a ratio of a PhysicalDownlink Shared Channel (PDSCH) energy per resource element to a CSIreference symbol (CSI-RS) energy per resource element, wherein theselected parameter is selected from a range having a minimum valuecorresponding to a ratio below −8 dB.
 5. The radio access network nodeof claim 3, wherein the processing circuit is configured to use thetransceiver circuit to signal to the UE, for configuring the UE to sendthe CSI report, a selected parameter indicating a ratio of a PhysicalDownlink Shared Channel (PDSCH) energy per resource element to acell-specific reference symbol (CRS) energy per resource element,wherein the selected parameter is selected from an extended range havinga minimum value corresponding to a ratio below −6 dB.
 6. The radioaccess network node of claim 5, wherein the extended range has a minimumvalue corresponding to a ratio of about −19.21 dB.
 7. A user equipment(UE) configured to support the transmission of multi-user superpositiontransmissions, where multi-user superposition transmission comprisestransmitting, in each of a plurality of time-frequency resourceelements, a modulation symbol intended for the UE and a modulationsymbol intended for a second UE, using the same antennas and the sameantenna precoding, the UE comprising: a transceiver circuit configuredto send and receive transmissions; and a processing circuit configuredto: receive one or more configuration messages from a radio accessnetwork node, via the transceiver circuit, the one or more configurationmessages directing the UE to transmit a channel-state information (CSI)report, the one or more configuration messages comprising at least oneof (a) a selected parameter indicating a ratio of a Physical DownlinkShared Channel (PDSCH) energy per resource element to a CSI referencesymbol (CSI-RS) energy per resource element, wherein the selectedparameter is selected from a range having a minimum value correspondingto a ratio below −8 dB, or (b) a selected parameter indicating a ratioof a Physical Downlink Shared Channel (PDSCH) energy per resourceelement to a cell-specific reference symbol (CRS) energy per resourceelement, wherein the selected parameter is selected from an extendedrange having a minimum value corresponding to a ratio below −6 dB; send,using the transceiver circuit, a channel-state information (CSI) report,in accordance with the one or more configuration messages; wherein thetransceiver circuit is further configured to receive a multi-usersuperposition transmission from the radio access network node.
 8. Aradio access network node configured to support the transmission ofmulti-user superposition transmissions, where multi-user superpositiontransmission comprises transmitting, in each of a plurality oftime-frequency resource elements, a modulation symbol intended for afirst user equipment (UE) and a modulation symbol intended for a secondUE, using the same antennas and the same antenna precoding, the radioaccess network node comprising: a transceiver circuit configured to sendand receive transmissions; and a processing circuit configured to:receive, via the transceiver circuit, multiple channel-state information(CSI) reports from the first UE for a first reporting instance, whereinone or more of the received multiple CSI reports correspond to one ormore respective multi-user superposition transmission states; anddetermine whether to use multi-user superposition transmission or anorthogonal multiple access transmission for scheduling the first UE in afirst scheduling interval, based on the received multiple CSI reports.9. The radio access network node of claim 8, wherein the processingcircuit is configured to first send one or more configuration messages,via the transceiver circuit, to the first UE, the one or moreconfiguration messages directing the first UE to provide multiplechannel state information (CSI) reports for at least the first reportinginstance such that one or more of the multiple CSI reports correspond toone or more respective multi-user superposition transmission states fora transmission to the first UE.
 10. The radio access network node ofclaim 9, wherein the multiple CSI reports are received on request, inresponse to the one or more configuration messages.
 11. The radio accessnetwork node of claim 8, wherein the processing circuit is configured toschedule the first UE based on said determining whether to usemulti-user superposition transmission or an orthogonal multiple accesstransmission, and to send a scheduling message, via the transceivercircuit, to the first UE.
 12. The radio access network node of claim 8,wherein a first one of the received multiple CSI reports comprises achannel quality indicator (CQI) corresponding to a full-power orsubstantially full-power data transmission to the first UE, and whereinthe processing circuit is configured to determine whether to usemulti-user superposition transmission or an orthogonal multiple accesstransmission by being configured to: obtain a CSI report from a secondUE, the CSI report from the second UE comprising a CQI corresponding toa full-power or substantially full-power data transmission to the secondUE; and determine that multi-user superposition transmission to thefirst and second UEs is feasible by being configured to determine thatsaid CQI for the first UE is greater than said CQI for the second UE bya predetermined factor or threshold, and determine that a precodermatrix indicator (PMI) corresponding to the CSI report from the secondUE matches at least one PMI corresponding to one of the receivedmultiple CSI reports from the first UE other than said first one of thereceived multiple CSI reports.
 13. The radio access network node ofclaim 12, wherein the processing circuit is configured to obtain the CSIreport from the second UE by being configured to: transmit, in aninterference measurement resource (IMR) for the second UE, aninterference component corresponding to a potential power shareallocated to the first UE in a multi-user superposition transmission tothe first and second UEs, wherein said interference component istransmitted using the same antennas and the same antenna precodingintended for the multi-user superposition transmission to the first andsecond UEs; and receive, from the second UE, said CQI corresponding to afull-power or substantially full-power data transmission to the secondUE, wherein said CQI reflects the interference component transmitted inthe IMR for the second UE.
 14. The radio access network node of claim 8,wherein the received multiple CSI reports from the first UE correspondto different power-sharing hypotheses for multi-user superpositiontransmission to the first UE.
 15. The radio access network node of claim14, wherein one or more configuration messages sent to the first UEindicate one or more of the different power-sharing hypotheses.
 16. Theradio access network node of claim 8, wherein the received multiple CSIreports from the first UE correspond to different ranks for datatransmission to the first UE.
 17. The radio access network node of claim16, wherein one or more configuration messages sent to the first UEindicate a number of channel quality indicators (CQIs) to be reported bythe first UE, each CQI corresponding to a different rank for datatransmission to the first UE.
 18. The radio access network node of claim17, wherein one or more configuration messages sent to the first UEindicate the number of CQIs to be reported by the first UE byindicating, for each desired CSI report, a corresponding transmissionrank by indicating a set of precoders that are restricted to thecorresponding transmission rank.
 19. The radio access network node ofclaim 8, wherein the received multiple CSI reports from the first UEcomprise N CSI reports, the N CSI reports comprising the N best channelquality indicators (CQIs) and wherein each of the N CSI reports includesa corresponding precoding matrix indicator (PMI) and rank indicator(RI).
 20. A first user equipment (UE) configured to support thetransmission of multi-user superposition transmissions, where multi-usersuperposition transmission comprises transmitting, in each of aplurality of time-frequency resource elements, a modulation symbolintended for the first UE and a modulation symbol intended for a secondUE, using the same antennas and the same antenna precoding, the first UEcomprising: a transceiver circuit configured to send and receivetransmissions; and a processing circuit configured to: receive one ormore configuration messages, the one or more configuration messagesindicating number of channel quality indicators (CQIs) to be reported bythe first UE, each CQI corresponding to a different rank for datatransmission to the first UE; and send, via the transceiver circuit,multiple CSI reports for a first reporting instance, wherein one or moreof the transmitted multiple CSI reports correspond to one or morerespective multi-user superposition transmission states.
 21. The firstUE of claim 20, wherein the one or more configuration messages directthe first UE to provide multiple channel state information (CSI) reportsfor at least the first reporting instance such that one or more of themultiple CSI reports correspond to one or more respective multi-usersuperposition transmission states for a transmission to the first UE.22. The first UE of claim 21, wherein the processing circuit isconfigured to send the multiple CSI reports on request, in response toreceiving the one or more configuration messages.
 23. The first UE ofclaim 20, wherein the processing circuit is configured to receive ascheduling message based on the sent multiple CSI reports, thescheduling message scheduling a multi-user superposition transmission tothe first UE.
 24. The first UE of claim 20, wherein a first one of thesent multiple CSI reports comprises a channel quality indicator (CQI)corresponding to a full-power or substantially full-power datatransmission to the first UE.
 25. The first UE of claim 20, wherein thesent multiple CSI reports correspond to different power-sharinghypotheses for multi-user superposition transmission to the first UE.26. The first UE of claim 25, wherein one or more configuration messagesreceived by the first UE indicate one or more of the differentpower-sharing hypotheses.
 27. The first UE of claim 20, wherein the sentmultiple CSI reports correspond to different ranks for data transmissionto the first UE.
 28. The first UE of claim 20, wherein the one or moreconfiguration messages received by the first UE indicate the number ofCQIs to be reported by the first UE by indicating, for each desired CSIreport, a corresponding transmission rank by indicating a set ofprecoders that are restricted to the corresponding transmission rank.29. The first UE of claim 20, wherein the sent multiple CSI reportscomprise N CSI reports, the N CSI reports comprising the N best channelquality indicators (CQIs) and wherein each of the N CSI reports includesa corresponding precoding matrix indicator (PMI) and rank indicator(RI).